sanitizer: Use glibc _thread_db_sizeof_pthread symbol if present

sanitizer: Use glibc _thread_db_sizeof_pthread symbol if present

I've cherry-picked following fix from llvm-project.  Recent glibcs
have _thread_db_sizeof_pthread symbol variable which contains the
size of struct pthread, so that sanitizers don't need to guess that
and risk that it will change again.

2022-02-15  Jakub Jelinek  <jakub@redhat.com>

	* sanitizer_common/sanitizer_linux_libcdep.cpp: Cherry-pick
	llvm-project revision ef14b78d9a144ba81ba02083fe21eb286a88732b.

(cherry picked from commit c4c0aa60891daeb4ea5a7c265bd681038f6d8271)